1. Field of Invention
The present invention relates to a driving device and, in particular, to a driving device of a brushless DC motor for a fan, wherein the driving device has a switch power conversion unit.
2. Related Art
FIG. 1 is a schematic illustration showing a conventional brushless DC motor and a driving device thereof. Referring to FIG. 1, a driving device 2 has a rectifier element 21, a filter element 22, a voltage clamping circuit 23 and a control element 24.
The rectifier element 21 receives an alternating current (AC) power AC and rectifies the AC power AC into a pulsating DC power. The filter element 22 filters the pulsating DC power to obtain a more stable direct current (DC) power DC to drive a brushless DC motor 1. In addition, the DC power is inputted to the voltage clamping circuit 23, which outputs a low-voltage auxiliary power to the control element 24. The driving device 2 adjusts the rotating speed of the brushless DC motor 1 by adjusting a pulse width modulation (PWM) signal outputted from the control element 24.
The conventional driving device 2 has the advantage of the simpler circuit design. However, since the driving device 2 rectifies and filters the AC power using the rectifier element 21 and the filter element 22 and directly outputs the DC power to the brushless DC motor 1, the stability of the power provided to the brushless DC motor is affected when the AC power becomes unstable. In addition, the driving device 2 only can convert the AC power into the DC power, but cannot change the voltage level according to the requirement. In other words, the driving device 2 cannot be applied to the AC power with the wider voltage range, and the brushless DC motor 1 only can be applied to the high-voltage operation mode but cannot be applied to the low-voltage operation mode.
Furthermore, the driving device 2 utilizes the voltage clamping circuit 23 to decrease the high-voltage DC power to the low-voltage auxiliary power. However, the voltage clamping circuit 23 causes the very high power loss.
Therefore, it is an important subject of the present invention to provide a driving device of a brushless DC motor for a fan, wherein the power of driving the brushless DC motor can be stably provided, the range of the operation voltage of the driving device can be broadened, and the power loss can be avoided.